Commit cbe9a51518db6f4e77a4f8c72e8cd9cd02fa7f49 | zig

author	Andrew Kelley <andrew@ziglang.org> 2020-01-21 22:01:24-05:00
committer	Andrew Kelley <andrew@ziglang.org> 2020-01-21 22:02:13-05:00
log	cbe9a51518db6f4e77a4f8c72e8cd9cd02fa7f49
tree	9efdeb5bcc24f2cbafec863ee422eede660b2c7c
parent	830e0ba2d27b55f999a891d007b24131b790e8c9
signature	Commit is signed but in an unrecognized format.

don't trust llvm's GetHostCPUName

comment from this commit reproduced here:

I have observed the CPU name reported by LLVM being incorrect. On
the SourceHut build services, LLVM 9.0 reports the CPU as "athlon-xp",
which is a 32-bit CPU, even though the system is 64-bit and the reported
CPU features include, among other things, +64bit.
So the strategy taken here is that we observe both reported CPU, and the
reported CPU features. The features are trusted more; but if the features
match exactly the features of the reported CPU, then we trust the reported CPU.

2 files changed, 35 insertions(+), 12 deletions(-)

lib
- std
  - target.zig
src-self-hosted
- stage1.zig

lib/std/target.zig+4

 @@ -637,6 +637,10 @@ pub const Target = union(enum) {
                 pub fn asBytes(set: *const Set) *const [byte_count]u8 {
                     return @ptrCast(*const [byte_count]u8, &set.ints);
                 }
+                pub fn eql(set: Set, other: Set) bool {
+                    return mem.eql(usize, &set.ints, &other.ints);
+                }
             };
             pub fn feature_set_fns(comptime F: type) type {

src-self-hosted/stage1.zig+31-12

 @@ -540,27 +540,25 @@ export fn stage2_progress_update_node(node: *std.Progress.Node, done_count: usiz
     node.context.maybeRefresh();
 }
+/// I have observed the CPU name reported by LLVM being incorrect. On
+/// the SourceHut build services, LLVM 9.0 reports the CPU as "athlon-xp",
+/// which is a 32-bit CPU, even though the system is 64-bit and the reported
+/// CPU features include, among other things, +64bit.
+/// So the strategy taken here is that we observe both reported CPU, and the
+/// reported CPU features. The features are trusted more; but if the features
+/// match exactly the features of the reported CPU, then we trust the reported CPU.
 fn cpuFeaturesFromLLVM(
     arch: Target.Arch,
     llvm_cpu_name_z: ?[*:0]const u8,
     llvm_cpu_features_opt: ?[*:0]const u8,
 ) !Target.CpuFeatures {
-    if (llvm_cpu_name_z) |cpu_name_z| {
-        const llvm_cpu_name = mem.toSliceConst(u8, cpu_name_z);
-        for (arch.allCpus()) |cpu| {
-            const this_llvm_name = cpu.llvm_name orelse continue;
-            if (mem.eql(u8, this_llvm_name, llvm_cpu_name)) {
-                return Target.CpuFeatures{ .cpu = cpu };
-            }
-        }
-    }
     var set = arch.baselineFeatures();
     const llvm_cpu_features = llvm_cpu_features_opt orelse return Target.CpuFeatures{
         .features = set,
     };
+    const all_features = arch.allFeaturesList();
     var it = mem.tokenize(mem.toSliceConst(u8, llvm_cpu_features), ",");
     while (it.next()) |decorated_llvm_feat| {
         var op: enum {
 @@ -577,7 +575,7 @@ fn cpuFeaturesFromLLVM(
         } else {
             return error.InvalidLlvmCpuFeaturesFormat;
         }
-        for (arch.allFeaturesList()) |feature, index| {
+        for (all_features) |feature, index| {
             const this_llvm_name = feature.llvm_name orelse continue;
             if (mem.eql(u8, llvm_feat, this_llvm_name)) {
                 switch (op) {
 @@ -588,6 +586,27 @@ fn cpuFeaturesFromLLVM(
             }
         }
     }
+    if (llvm_cpu_name_z) |cpu_name_z| {
+        const llvm_cpu_name = mem.toSliceConst(u8, cpu_name_z);
+        for (arch.allCpus()) |cpu| {
+            const this_llvm_name = cpu.llvm_name orelse continue;
+            if (mem.eql(u8, this_llvm_name, llvm_cpu_name)) {
+                // Only trust the CPU if the reported features exactly match.
+                var populated_reported_features = set;
+                populated_reported_features.populateDependencies(all_features);
+                var populated_cpu_features = cpu.features;
+                populated_cpu_features.populateDependencies(all_features);
+                if (populated_reported_features.eql(populated_cpu_features)) {
+                    return Target.CpuFeatures{ .cpu = cpu };
+                } else {
+                    return Target.CpuFeatures{ .features = set };
+                }
+            }
+        }
+    }
     return Target.CpuFeatures{ .features = set };
 }